1. Field of the Invention
The present invention relates to an airbag device provided with an airbag, which is expanded and inflated by admitting an inflating gas.
2. Description of the Related Art
In the related art, an airbag device includes an airbag and an inflator housed in the airbag (JP-A-2001-114060). In this airbag device, the airbag is provided with an airbag body forming a bag-shaped outer peripheral wall, and a reinforcing cloth. The reinforcing cloth is arranged on the outer peripheral wall of a portion in the airbag body on the upstream side of the inflating gas. This reinforcing cloth is provided for preventing the gas leakage due to the heat, the pressure or the like which is generated when the inflator is activated, and is arranged to enclose the inflator. Moreover, the reinforcing cloth is sewn at its peripheral edge substantially all over the outer peripheral wall of the airbag body. Usually in this airbag device, at the time of expanding the airbag, the airbag body admits the inflating gas from its downstream portion and inflates the upstream portion apart from the inflator to a large size.
In the airbag device thus constructed, however, the peripheral edge of the reinforcing cloth is sewn substantially in its entirety to the outer peripheral wall of the airbag body. In other words, the outer peripheral wall of the portion in the airbag body on the upstream side of the inflating gas is sewn together with the reinforcing cloth. Therefore, the outer peripheral wall at the portion in the airbag body on the upstream side of the inflating gas is difficult to expand when the airbag inflates so that only the outer peripheral wall at the portion on the downstream side is extended in the direction of the inflating gas. Further, a high tensile stress is applied to the outer peripheral wall forming the downstream portion. If the output of the inflator is increased the more to shorten the time period for the airbag to complete its inflation, for example, the tensile stress to be applied to the outer peripheral wall forming the downstream portion grows even more. With this construction, moreover, if a tether or the like is sewn to the outer peripheral wall of the portion in the airbag body on the downstream side of the inflating gas, the stress concentration may occur in the outer peripheral wall or the portion to be sewn to the tether, and the outer peripheral wall of the airbag may be damaged.
In the airbag device thus constructed, moreover, the airbag is provided with an airbag body and a band-shaped tether made of a flexible cloth member.
The tether has its two lengthwise end portions acting as joint ends to be joined to the airbag body, and regulates the shape of the airbag body having completed its inflation. In other words, the tether in the airbag described in the aforementioned patent is arranged to regulate the thickness of the airbag body and so maintain the plate shape of the airbag body.
However, the tether is subject to a high tension when the airbag body completes its inflation, so that it is easily broken at its end joints.